Lincoln was on a relatively short list of conservative Democrats whom conservatives hoped could be persuaded to cross over and vote against Kagan. So far, only Sen. Ben Nelson (D-Neb.) has come out against Kagan. And with the Senate set to vote on the nomination Thursday, time is short.

As recently as this morning, Sen. Jeff Sessions (R-Ala.) was on the Senate floor pleading with Democrats to break ranks.

"Some raise the question of how many Republicans will vote for the nominee. Another question to ask is how many Democrats will vote against the nominee," Sessions said.

So far, the answer to the first question is: five. And at the moment, it looks increasingly like one is going to be the answer to that latter question.